zeroone.io is a web experiment in which visitors are invited to randomly click 0 or 1, collectively generating an abstruse binary stream.

I really like that it gives live feedback showing *your* contribution and how even if you keep pressing just one of the two buttons, your additions are interwoven with others (so the timing disrupts the pattern). Also a nice spin on the eternal question of how random is random (in a mathematical sense, in a computational sense, in a social sense).